The present invention relates to an angle position detection apparatus that incorporates a plurality of VR resolvers, and relates in particular to an improved technique appropriate for reducing the size and the thickness of a direct drive motor, while providing a high angle position detection accuracy.
Since a direct drive motor for which no speed reducer is provided can drive a load directly and can perform accurate positioning without backlash or lost motion, such a motor can be used for various applications, including an index table for an NC machine tool, a carrier device, or a robot arm for an assembly device. For these reasons, efforts are made to develop a smaller direct drive motor that can provide more accurate positioning. To this end, an improved technique is proposed in JP-A-6-46552 (Patent document 1). According to this technique, a blocking member that magnetic flux can not easily pass is located between a unipolar resolver and a multipolar resolver, which are incorporated in the motor housing of a direct drive motor, so that neither resolver will be affected by magnetic interference produced by the leakage of magnetic flux from the other. With this configuration, accurate positioning is ensured.
[Patent document 1]
JP-A-6-46552
However, when a blocking member is arranged in the gap between the resolvers, the size of the internal space required to install the resolvers in the motor housing is increased, and reducing the size and the thickness of the direct drive motor is difficult. On the other hand, the size and the thickness of the direct drive motor can easily be reduced by removing the blocking member; but if this is done, magnetic flux would leak from the adjacently located resolvers and the detection accuracy would be degraded.